<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" 
            @click="handleLetterClick" 
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd" :ref="item">
            {{item}}
        </li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    computed: {
        letters() {
            const letters = [];
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data() {
        return {
            touchStatus: false,
            startY: 0,
            // 节流
            timer: null

        }
    },
    updated() {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick(e) {
            // console.log(e.target.innerText);
            this.$emit('change', e.target.innerText)
        },

        handleTouchStart() {
            this.touchStatus = true
            
        },
        handleTouchMove(e) {
            if (this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 79
                // console.log(touchY);
                const index = Math.floor((touchY - this.startY) / 20)
                // console.log(index);
                if (index >= 0 && index <= this.letters.length) {
                    this.$emit('change', this.letters[index])
                }
                }, 16)
                
            }
        },
        handleTouchEnd() {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
    @import '~@/assets/styles/varibles.styl';
    .list
        display flex
        flex-direction column
        justify-content center
        position absolute
        right: 0
        top 1.58rem
        bottom 0
        width: .4rem
        .item
            text-align center
            line-height .44rem
            color $bgColor
</style>